The present invention is directed to an easy-open structure for containers and a method of forming the same. More particularly, the invention relates to an easy-open structure for containers and a method of forming the same wherein a sheet material container wall panel such as a container end has a scoreline formed therein outlining a movable wall portion adapted to be moved out of conforming contour with the remainder of the sheet material wall panel with an elongated tab opener.
In known, commercially-used, easy-open structures for containers of the aforementioned type, the tab opener is generally secured to the sheet material container wall panel by a rivet head which is press formed from the sheet material wall panel as in U.S. Pat. No. 4,257,529, for example. In such arrangements, the tab opener functions as a lever during opening when a handle end of the tab opener is lifted to pivot the tab opener vertically about the rivet which serves as the fulcrum. The space requirements and stresses placed upon the sheet material during rivet formation prevent the rivet from being located in close spaced relationship to a portion of the scoreline where tearing is initiated with movement of the tab opener. This results in a relatively low mechanical advantage lever action where the length of the tab opener is limited by space and/or cost requirements. The relatively large size of the rivet head also adversely effects the mechanical advantage of the lever action. Thus, these known structures are disadvantageous in that they can be relatively difficult to open, requiring the application of considerable force to lift the tab opener. The relatively small size of the handle end of the tab opener in proportion to the size of the tab opener can also make it difficult to open. The use of a rivet to secure the tab opener to the container wall panel is further disadvantageous in that it imposes restrictions on the type of material that can be used for the sheet material wall panel. That is, a material must be relatively soft or ductile to form a rivet head therein thereby precluding the use of relatively hard, higher strength materials and requiring the use of relatively thick sheet material to meet minimum strength requirements. In addition, in those applications where it is required to coat the inside of the easy-open container end, press forming the rivets can damage the coating on the end thereby necessitating a coating operation after the tab opener is joined to the end.
There have been attempts to avoid some or all of the aforementioned disadvantages associated with the use of rivet connections between tab openers and associated container wall panels. In U.S. Pat. Nos. 3,084,835 and 3,334,778, for example, structures and methods are disclosed wherein the tab opener is electrically resistance spot welded to the container wall panel. However, electrical resistance spot welding has not been widely adopted by the industry, in part, because of the difficulty in controlling the weld quality, the large heat affected zone causes weakness around the weld spot, and the necessity of using current conducting electrodes to forceably engage the workpieces at the weld zone. Such electrodes can be easily contaminated by various coatings. Coatings frequently present on the workpieces may also prohibit the use of electrical resistance spot welding such as with tin free steel due to the high resistance surface. Where coated workpieces can be resistance spot welded, undesirable damage to the coating can occur thus requiring a repair or postweld coating operation.
Another method which has been proposed is to join the tab opener to the container wall panel by drawn arc welding as in U.S. Pat. No. 3,483,355. However, such a method requires the additional manufacturing step of forming an attaching dimple or projection in the tab opener in order to localize the welding current at a single spot to effect welding. The heat effected zone from this process is also quite large and damaging to spot strength. A coating on the inner surface of the container wall panel can also be damaged during such a process thereby making it necessary to employ a coating operation subsequent to welding.
An object of the present invention is to provide an improved easy-open structure for containers of the aforementioned type and a method of forming the same which avoid the above-discussed problems associated with rivet attachment and the known alternatives thereto. More particularly, an object of the present invention is to provide an easy-open structure for containers of the type described which provides greater mechanical advantage lever action during tear initiation than the riveted structures and is therefore easier to open.
A further object of the invention is to provide an easy-open structure for containers which need not be formed from the soft, ductile materials necessary for rivet-formation so that harder, higher strength materials can be employed thereby permitting the use of thinner materials and reducing costs.
An additional object of the invention is to provide a method of forming an improved easy-open structure for containers which can be used to join plain or coated workpieces in most instances, including those with non-conductive or high resistive coatings, and which can be used to join such workpieces without damaging a coating on the inner surface of the container wall panel thereby eliminating the requirement of a coating operation subsequent to welding.
These and other objects are attained by the method of forming an easy-open structure for containers according to the invention which comprises the steps of providing a sheet material wall panel having a scoreline formed therein outlining a movable wall portion which is adopted to be moved out of conforming contour with the remainder of the sheet material wall panel, providing a tab opener for moving the movable wall portion out of conforming contour with the remainder of the wall panel, and welding the tab opener to the movable wall portion with a high energy density welding process wherein the energy density is at least on the order of 10.sup.6 watts/inch.sup.2. According to a preferred embodiment of the invention, the high energy density welding process is a laser welding process.
The high intensity or energy density, at least on the order of 10.sup.6 watts/inch.sup.2, which can be achieved by optically focusing a laser beam permits very rapid welding of the tab opener to the movable wall portion of the sheet material wall panel and produces only a relatively small weld heat affected zone thereby minimizing degradation of sheet material properties during welding as compared with those welding techniques which have heretofore been employed or proposed in forming easy-open structures for containers. These advantages, and the ability to focus the laser beam to a relatively small spot size, such as 0.010 inch diameter or less, as well as the fact that there is no need for mechanical contact of any kind with the workpiece in the immediate weld area, enable the weld area to be in close spaced relationship to a portion of the scoreline where tearing is initiated with movement of the tab opener. This permits the mechanical advantage of the lever action to be increased thereby making it easier to open the container. According to a disclosed embodiment the weld area is located within approximately 1/8th inch or less from the scoreline. Coated workpieces can be laser welded in most instances. The laser can also be precisely controlled so that a tab opener can be welded to the outer side of a movable wall portion of a sheet material wall panel without damaging a coating on the inner side thereof. In this latter case the weld penetration extends only partially through the thickness of the wall portion and postweld coating of the inner side of the wall panel can be avoided.
An improved easy-open structure for containers according to one embodiment of the invention comprises a sheet metal container wall panel having a scoreline formed therein outlining a movable wall portion to be moved out of conforming contour with the remainder of the sheet metal wall panel, and an elongated tab opener for moving the movable wall portion out of conforming contour with the remainder of the wall panel. The tab opener is welded to the movable wall portion at an elongated weld area extending transverse to the longitudinal direction of the tab opener and in close spaced relationship to a portion of the scoreline where tearing is initiated with movement of the tab opener. The elongated weld area is formed by a high energy density welding process, that is, laser welding, wherein the energy density is at least on the order of 10.sup.6 watts/inch.sup.2.
By providing an elongated weld area between the tab opener and the wall panel, it is possible to reduce the size of the connection from a single, relatively large diameter annular rivet or weld to a relatively narrower elongated connection or weld area which enhances the mechanical advantage of the lever action and ensures proper alignment of the force at the working end of the tab opener, in the case of Class 1 lever action, for example. With laser welding the welds can also be consistently placed in close spaced relationship to the scoreline to maximize the mechanical advantage of the lever action and no special surface indentations in the tab opener are required to localize the welding energy.
According to one form of the invention, the elongated weld area includes a continuous elongated laser weld which extends transverse to the longitudinal direction of the tab opener. In another form of the invention the elongated weld area includes a plurality of laser welds positioned in spaced relationship along the length of the weld area.
In several of the disclosed embodiments, one end of the elongated tab opener serves as a handle for moving the movable wall portion out of conforming contour with the remainder of the sheet the other end is a working end which is positioned over a portion of the scoreline where tearing is initiated. The tab opener is welded to the movable wall portion at an elongated weld area which is positioned in close spaced relationship to the working end of the tab opener and which serves as a fulcrum so that tearing can be initiated along the scoreline by Class 1 lever action with a relatively high mechanical advantage by lifting the handle end of the tab opener. The handle end of the tab opener is generally circular in form and has a central aperture through which a finger may be inserted after the handle end of the tab opener has been initially lifted.
As an additional feature, the easy-open structure for containers of the invention can be provided with means for venting the container as the handle end of the opener is lifted. In one disclosed embodiment the means for venting includes an additional weld area connecting the tab opener to a vent portion of the movable wall portion between the elongated weld area and the handle end of the tab opener whereby the vent portion is torn from the movable wall portion by a Class 2 lever action to vent the container upon lifting the handle end of the tab opener. An additional scoreline may be formed in the movable wall portion around this additional weld area to outline the vent portion. Rupture occurs along this additional scoreline when the vent portion is torn from the movable wall portion.
In one form of the invention the wall panel is a container end and the movable wall portion thereof extends over essentially the entire container end. The movable wall portion is completely circumscribed by a scoreline so that it may be removed from the container end. In another form of the invention the wall panel is a container end and the movable wall portion is in the form of a tab which encompasses only a portion of the container end so as to define a drinking or pouring opening in the case of a beverage can, for example. The scoreline does not completely circumscribe the tab so that a hinge metal portion remaining for retaining the tab and tab opener on the container end after opening.
As another feature of the invention the score line may be formed essentially or entirely through the thickness of the sheet metal container wall panel so that the movable wall portion can be easily moved out of conforming contour with the remainder of the sheet metal wall panel. A coating can be applied to at least the inner side of the sheet metal container wall panel in the area of the scoreline for resisting leakage through the container wall panel at the scoreline. To resist undesired outward or inward movement of the movable wall portion from pressures within a container, the tab opener is welded to the sheet metal container wall panel at a plurality of spaced locations about the movable wall portion by means of a high energy density welding process. The weld sizes at the spaced locations are relatively small to allow breaking thereof during opening. In one such embodiment the easy-open structure for containers comprises a tab opener which is provided with handle means adjacent one end thereof for moving the movable wall portion out of conforming contour with the remainder of the sheet material wall panel, the tab opener being welded adjacent a second end thereof opposite said one end to the sheet material container wall panel by means of a high energy density welding process to provide a fulcrum. The tab opener is welded at a location intermediate its ends to the movable wall portion whereby tearing along the scoreline is initiated by Class 2 lever action upon lifting the tab opener with the handle means. In another, similar embodiment, the second end of the tab opener is located in the vicinity of a hinge material portion connecting the movable wall portion to the sheet material wall with this second end of the tab opener serving as a fulcrum during opening by a Class 2 lever action.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the invention.